1. Field of the Invention
This invention relates to a locking pliers and, more particularly, to a locking pliers that can be held firmly in a closed and locked position without the continuous application of force by a user while tightly gripping a workpiece.
2. Description of the Related Art
Referring to FIG. 1, a conventional locking pliers 10 disclosed in U.S. Pat. No. 7,861,622 B2 is shown to include a fixed handle 11 supporting a fixed jaw 12, a movable jaw 14 pivotally connected to the fixed handle 11 by a first pivot pin 13, a movable handle 16 pivotally connected to the movable jaw 14 by a second pivot pin 15, and a toggle-link locking mechanism 17 disposed to lock the movable jaw in a closed, locked position. The fixed handle 11 has an oval slotted aperture 111 such that the first pivot pin 13 is movable in the aperture 111 during use of the pliers 10. A long axis of the aperture 111 is arranged at an angle α with respect to a line extending through the center of the closed jaws 12 and 14. The angle α is approximately 15 degrees. The locking mechanism 17 has a link 173 pivotally connected to the movable handle 16 and in sliding and pivoting contact with an adjustment screw 171, and a biasing member 172 extending between the movable jaw 14 and the fixed handle 11 to bias the jaws 12 and 14 away from each other.
Referring to FIGS. 2 and 3, in operation, when the pliers is first locked onto a workpiece 20 and a turning force is applied to the pliers, the movable jaw 14 rotates clockwise around the second pivot pin 15 toward the fixed jaw 12 to allow a rearward movement of the first pivot pin 13 in the aperture 111. The movable jaw 14 is also moved rearward and toward the fixed jaw 12, as indicated by arrows 21 and 22, to increase the gripping force on the workpiece 20. Since the first pivot pin 13 is moved to a rear end of the aperture 111 when the jaws 12 and 14 are operated to the closed, locked position, the design of the aperture 111 is critical. However, the aperture 111 does not prevent a problem that a sliding engagement of the first pivot pin 13 with a wall defining the aperture 111 may be unstable. Therefore, the gripping force on the workpiece 20 is adversely affected. In addition, the aperture 111 has to be made precisely. If the axis of the aperture 111 suffers deviations from the angle α, the first pivot pin 13 can not move stably or even move rearward in the aperture 111.